System for the transmission of motion



Feb. 26, 1946. D, MgTCHE-LL SYSTEM FOR THE TRANSMISSION oF MOTION' 2 sheets-sheet 1 Filed Nov. 2, 1942 /Nl/E N TOR By D. M/ TCHEL L ,44 fhig i ATTORNEY Feb- 26, 1946-.V D. MITCHELL SYSTEM FOR THE TRANSMISSION OF MOTION Filed Nov. 2I 1942 2 Sheets-Sheet 2 E hm :E Bw v lli l .13%. AE Q ,/M/E/vro@ By 0. M/TCHELL JT u;

ATTORNEY ,Ill

Patented F 1946 SYSTEM FOR THE TRANSMISSION OF I MOTION Deren Machen, Bound amr, N. ,1., assigner t Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 2, i942, serial 10.464.271 `7 claims. (cl. i12-239i This invention relatesl to electrical systems for the transmission of movements and more specifically to systems in which circular motion produced by turning a dial or other rotary member at one point is very accurately and automatically reproduced at a distant point.

Various methods are known for remote automatic reproduction of circular motion, such as that produced, for example, by turnira dial. Two very well known methods of producing this result respectively utilize direct current land Selsyn motors. Theysystems using these methods work very well over comparatively short distances but they are not very practical in operation over long lines. The need sometimes arises, as in the control of guns from distant points, for a highly accurate system for reproducing angular motion over comparatively long distances, The present invention has for its principal object the provision of such an electrical system.

In accordance with the invention, this object is attained by producing at the transmitting station two waves of different frequencies, obtaining therefrom a -wave having a frequency which is the difference between the frequenciesof the original waves, utilizing this derived wave` to obtain a direct current signal the amplitude of which is proportional to the frequency of the derived wave, and opposing this direct current signal by a second direct current signal produced at the distant station which is representative ofthe difference in frequency between two waves of different frequency the frequency difference of which is dependent upon the position of the member whose position it is desired to make correspond with that of the member at the sending station, the position of said member being determined by the combined effect of the opposed direct current signals.

In the specific embodiment oi' the invention chosen by way of example for illustrative purposes, a motor -drives the rotating member at the receiving station until the direct current signal representing the position of the rotating member at the receiving station equals that of the direct current signal representing Ithe position of the rotating member at the sending station, at which point no further rotation of the member at the receiving station takes place. Since frequency difference (or the two frequencies themselves) is the only information which has to be transmitted, the effects of amplitude variation in any circuit or carrier system may be made negligible, in accordance with well known practice in the transmission of frequency modulated carrier waves, by amplitude limiting. By keeping the two frequencies produced at the sending station close together, and near the middle of the telephone band, for example, the effects of delay distortion are made so small as to be almost v negligible. Due to the fact that a motor at the l receiving station is used to drive the rotating member at that station, there is no practical lim itation to the amount of torque that can be delivered at the distant point. For this reason the arrangement 4has a marked advantage in such remote-controly operations as gun-pointing, tel--v autography, etc.

In this embodiment of the invention, a variable condenser containing a fixed and a rotating eletating element being mechanically connected to the diai or other' rotary member whose circular motion it is desired lto reproduce at a distant receiving station. The rotation of this portion of the condenser varies the condenser capacitance and as the condenser is included in the tuned` circuit of an oscillator, the output frequency of the oscillator is varied. The output waves of this oscillator are preferably applied to a line, which may be either a telephone line or a radio channel, along with the output waves from a second oscillator, this one of fixed frequency. Preferably, the output waves of the second oscillator have a frequency which is. within the audio range while the frequency of the output waves of the first oscillator varies from a value which is just greater than the frequency of the second oscillator to a value which is somewhat less than twice the frequency of the second oscillator. At the far end of the line, that is, at the receiving station, the waves from the first and second oscillators are applied to a modulator in the output circuit of which is connected a low-pass lter which passes frequencies corresponding to the difference between the waves of the nrst and second oscillators but which will cut oiT frequencies corre- 1 spending to thosel of the waves from these two oscillators. This difference frequency wave is then applied to a volume limiter which is arranged to produce a substantially flat-top wave whose amplitude is independent of the amplitude of the received wave, This wave is then passed through a shaping network which causes the amplitude of its output wave to vary in accordance with the frequency of the signal from the volume limiter.. The output wave ofthe shaping network is then applied to a detector to produce an output signal which is applied to one winding 0f a diileiental relay. the other winding-of which is connected to the output of a circuit similar to that already described, which circuit is controlled by a condenser having a rotatable element driven by the movement of the rotary member at the receiving station whose angular movement is adapted to follow that of thedial or similar device of the sending station. The strength of the current in each winding of the differential relay is thus dependent only on the difference in frequency between the output -waves of the nxed frequency oscillator and of the variable frequency oscillator in the circuit feeding the winding. The two circuits respectively feeding the windings of the differential relay are made equal within very close limits so that if the two "difference frequencies are the same, the currents in the two windings of the differential relay are equal and hence the armature of the relay will not'be oper.. ated in either direction to operate a motor driving the rotatable element at the receiving end of the line. If the diierence frequency representing the position of the movable member at the transmitting station varies, however, the balance between the two windings of the relays is immediately upset and the motor will be operated in a direction to restore the balance. Obviously, either the two frequencies generated at the transmitting station or the difference between them may be transmitted to the receiving station.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which:

Fig. l1 is a schematic circuit diagram of the arrangement according to this invention; and

Fig. 2 is a more detailed circuit diagram of the arrangement shown in Fig. 1.

Referring more specifically to the drawings, Figs. 1 and 2 are circuit diagrams of an electrical system for the transmission of angular movement which is shown by way of example to illustrate the principles of the present invention. Fig. 1 is a schematic circuit diagram showing 'certain of the elements of the circuit in block diagram form while Fig. 2 is a more detailed circuit diagram of the arrangement shown in Fig. l. In accordance with the invention, it is desired to have the receiving rotor Ill follow the angular movement of the sending rotor I I. 'These two rotors may be, and in the usual case are, separated by a considerable distance and it is the purpose of the arrangement of this invention Ito have the receiving rotor I accurately follow the movement of the rotor II.

Referring now tothe sending station identined by the reference character S, the sending rotor II is connected by any suitable means to the rotating element I2 of the condenser I3, which condenser also has a nxed member I4. The condenser Il is included in the tuned circuit of a Hartley oscillator I which is well known to those skilled in the art. For a description of the Hartley oscillator, reference may be made to page 5l of the Radio Amateur's Handbook, Special Defense edition, 194.2. Variation of the capacitance of the condenser Il by the rotation of the movable member I2 thereof varies the frequency of the output waves which, for example, are applied by means of the coupling condenser Il and resistor I1 to a line or other channel L to the receiving station R.

A second oscillator 20, preferably of the same type as the oscillator l5 except that the condenser !I in the tuned circuit thereof has a fixed capacity, is included at the sending station. The

output waves of the oscillator 2li may be applied by means of the coupling condenser 22 and resistor il to the line or other channel L. By way of example, the oscillations from the oscillator 5 20 may have a frequency of about 800 cycle; per second while those from the oscillator Il may vary from a frequency of about v850 cycles per second to about 1,500 cycles per second. In the arrangement shown, both waves are applied to the line L without modulation but it is apparent that other arrangements are possible, as will be pointed out more fully below.

At the far end of the line, that is, at the receiving station R., one of the two waves is modulated by the other by any suitable modulator, such as the dry rectier bridge circuit 30. The modulation products are then conducted to a low-pass filter 3| which passes the component corresponding in frequency to the ,diiference between the frequency produced by the oscillations from the oscillator I5 (F1) and those from the oscillator (Fa) but which will not pass frequencies corresponding to Fi, F: or any harmonies thereof. `Tiuri it will be seen that prefershould have a frequency which varies from a value which is greater than the frequency of the second oscillator 20 to a value which is somewhat less than twice the frequency of the oscillator lil. It will thus be understood that the output of the low-pass filter II is a wave the frequency of which is the difference between the frequencies of the oscillators II and 20, or, in other words, is Fi-Fz.

The output wave of the filter lI is applied by any suitable means such as the transformer I2 to the amplifier and volume limiter circuit 8l comprising any suitable amplifier 34 and two parallel circuits 3l and I0. The circuit il comprises in series arrangement a source of potential "l1 and two rectiilers Il and 3l. The circuit comprises in series arrangement a source of potential and two rectifiers 4I and 42. The sources of potential 31 and 40, which are opposlteiy polarized with respect to the output wave in the amplifier 34, are adapted to bias the circuits ll and 3i so that no current flows therethrough luntil the output wave of the amplifier 34 exceeds a certain predetermined value, in 5 which case the parallel circuits 8B and become conducting to pass current. thus limiting any waves above said certain amplitude from being applied to the condenser 4I, which is of relatively small capacity, for example, 0.16 microfarad. and the resistor of the order of about 1,000

ohms. The resistor 44 and the capacitor 4I form a shaping network 4IA which causes, in a manner well known to those acquainted with frequency modulation practice, the amplitude of its output (l0-to vary in a predetermined manner according to the frequency of the signals from the limiter circuits Il and 30.

The output wave from the shaping network is then applied to an amplifier and detector 40 comprising any suitable amplifier 41 and a balanced detector comprising the bridge circuit 4I.

- The detector produces a pulsating direct current at its output which is smoothed out by condenser 49 and then applied to winding 8l of relay II, The amplitude of this direct current is dependent upon the amplitude of the wave applied to the input of the amplifier 41 which in turn is proportional to the frequency of the wave applied to the amplifier and volume limiter circuit Il. Direct current is also applied to a second ably the output waves of the nrst oscillator It assaut has been given the same reference character as.

the corresponding element of the ilrst circuit ex' cept that a prime has been added to the reference character.

'I'he relay 5I has an armature 53 which is adapted to be connected through a sourcek of potential 54 tofground andwhich is energized to make contact with one or the other of two contacts 55 and 55 depending on whether the current in coil 55 is stronger than that in coil 52 or vice versa. When no current is flowing in the coils 55 and 52 or when the currents in these two coils are equal, the armature 53 assumes a neutral position between the contacts 55 and 55. When the armature makes contact with either of contact elements 55, 55, the reversible drive mechanism 51 is energized in one direction or the other to rotate (either directlyvor through appropriatel gearing) the rotating element I2 of the condenser I3 in the proper direction to cause the output frequency of the oscillator I5 to change until the direct currents in the windings 55 and 52 are once again equal. 'I'he reversible drive mechanism 51 may be of any suitable form such as that shown in Fig. 2. The arrangement in this figure comprises a motor armature 55, a series field 55, a source of potential 55 and two relays 5| and 52, the contacts of which are normally open when the corresponding armature is not energized. As will be pointed out more fully below, when the relay 5I` is venergized the series field winding 59 is connected in one direction to the armature 55 which causes the motor to rotate in one direction while if the relay 52 is energized the series field winding is connected in the reverse direction to the armature 55 and causes the motor to rotate in the opposite direc.

tion.

The operation of the circuit shown in Figs. l and 2 is as follows: Let it beassumed that the. rotor of the condenser I3 is in such a position that the frequency of the oscillator l5 is 1,000 cycles and the position of the rotor I2 of the condenser I3 is such that the frequency of the oscillator I5' is also 1,000 cycles, the frequency of the oscillators 25 and 25' being constant at 800 cycles. Then the frequency passed by each.

of the filters 3| and 3|' is the difference frequency between the output wavesoil the oscillators I5 and 25 and i5 and 25 respectively, or 200 cycles. The tops of the 200-cycle waves are cut off by the volume limiters 33 and 35' making a series of flat top waves of both positive and negative amplitudes. These flat top waves are shaped in the shaping networks 45l and 45 to produce signals the amplitude of which varies with the frequency of the output waves of the filters 5I and 5|. If this frequency is high, the impedance of the condenser 45 (or 45') is small and the transmitted signal is large while if this frequency is small, the reverse is true. 'I'he output waves of the shaping networks 45 and 45 are amplified and detected by the apparatus 45 and 45' to produce two equal direct current signals applied respectively to the coils 55 and 52 of the relay 5|. Since these two currents are equal the armature 53 is held in its intermediate position, that is, in a position intermediate the contacts 55 and 55 and not contacting either of them. In this position, the motor forming part of the reversible drive 57| is not energized to move the rotor I2 of the condenser I3'.

Now let it be assumed that the sending rotor II is suddenly rotated in such a direction that the capacity of the condenser I3 is varied by an amount sufficient to cause the output wave of the oscillator I5 to be increased to 1,200 cycles per second. The output wave of the filter 5| is then 400 cycles, After this wave is passed through the volume limiter and the shaping network the output wave of the network has a larger amplitude than it had previously when frequency F1 was 1,000 cycles. The current in the coil is therefore larger than that in the lcoil 52 and the armature 53 is attracted towards the contact 55 thus energizing the relay 5I and causing its contacts to close and complete a circuit through which current iiows from the source of direct potential 55 throughl series winding 55 from terminal B to terminal A, the first contact the current in the coil 52 until a balance has been obtained again between the currents in the coils 55 and 52. i When this balance is obtained the receiving rotor I5 is in a position once again corresponding tothe position of the sending rotor |I.

Now i!!4 the sending rotor II is turned in a direction opposite to that assumed in the preceding paragraph the frequency of the oscillator I5 is reduced, for example to 900 cyc1es;vthefrequency passed by the low-pass lter 5I becomes 100 cycles which when acted upon by the apparatus 33, 45 and 45 produces a smaller current in the coil 55 than in the coil 52. This causes the armature 5I to contact the contact element 55 closing the circuit to energize the relay 52. This completes a circuit through which current flows from source through the series winding 55 in 'a direction from B to A, the ilrst set of contacts of the relay 52, the armature 55 in the direction from terminal C to terminal D and the second set of contacts of the relay 52 back to the source 55. The motor is therefore energized in the direction opposite to that described .in the preceding paragraph and the rotor I2 is driven in the direction which tends to reduce the frequency of the output of oscillator I5', thereby decreasing the current inthe coil 52 until it becomes equal again to the coil 55, at which time the armature 53 is returned to its intermediate position and the receiving rotor I5 is in a posi\ "stead of thetwo frequencies produced by the oscillators I5 and 25. Moreover, the two members whose movements itis desired to synchronize need not be rotor members but may instead be any members having movement in opposite directions as, for example, a linear movement on one side or the other oi' a reference position. Moreover, the movement of the member at the sending station may vary the inductance or resistance in a suitable oscillator instead of causing variation of capacity as in the circuit arrangement shown. I

The arrangement of this invention may be used in any situation where it is desired to reproduce at one position the movement of a member at another, such as in a telautograph, metering, or gun-pointing.

Various other modifications may be made in the apparatus disclosed without departing from the spirit of the invention, the scope of which is indicated in the appended claims.

What is claimed is:

1. Apparatus for accurately producing by the movement of a member at a sending station a desired predetermined movement of a. member at a receiving station, comprising motor means for driving said member at the receiving station,

circuit means for producing a signal controlled by, and corresponding to the position of, said sending station member, a second circuit means for producing a signal controlled by, and corresponding to the position of, said receiving station member, and means simultaneously differentially responsive to the magnitude of said two signals for actuating said motor means, each of said circuit means comprising means for deriving a periodically varying voltage the frequency of variation of which is dependent at each instant upon the position of the one of said members controlling that circuit means, and means responsive to the frequency of said periodically varying voltage in that circuit for determining the magnitude of the signal in that circuit and controlling said differentially responsive means.

2. The combination of elements as in claim 1 in which the movement of each of said members yis rotary.

3. Apparatus for accurately producing by the movement of a member at a sending station a desired predetermined movement of a member at a receiving station, comprising motor means for driving said member at the receiving station, circuit means for producing a signal controlled by, and corresponding to the position of, said sending station member, a second circuit means for producing a signal controlled by, and corresponding to the position of, said receiving station member, and means simultaneously differentially responsive to the magnitude of said two signals for actuatin'g said motor means, each of said circuit means comprising means for deriving a voltage wave of fixed frequency, means for deriving a periodically varying voltage wave the frequency of variation of which is dependent at each instant upon the position of the oneof said members controlling that circuit means, means for modulating the wave of said first frequency with the wave of said second frequency, means for filtering the resultant modulated wave to produce a wave the frequency of which is equal to the difference between said two frequencies, and means responsive to said last-mentioned wave for determining' the magnitude of the signal in that circuit and controlling said diii'erentially responsive means.

4. The combination of elements as in claim 3 in which the frequency of said variable voltage wave is adapted to vary between a frequency which is slightly greater than the frequency of said fixed frequency voltage wave and a frequency which is less than twice the frequency of said fixed frequency wave.

5. Apparatusfor accurately producing by the movement of a member at a sending station a desired Vpredetermined movement of a member at a receiving station, comprising motor means for driving said member at the receiving station, circuit means for producing a signal controlled by, and`corresponding to the position of, said sending station member, a second circuit means for producing a signal controlled by, and corresponding to the position of said receiving station member, and means simultaneously differentially responsive to the magnitude of said two signals for actuating said motor means, each of said circuit means comprising means for deriving a voltage wave of xed frequency, means for deriving a periodically varying voltage wave the frequency of variation of which is dependent at each instant upon the position of the one of said members controlling that circuit means, means for modulating the wave of said first frequency with the wave of said second frequency, means for filtering the resultant modulated wave to produce a third wave the frequency of which is equal to the difference between said two frequencies, means for limiting the volume of said last-mentioned wave, means for shaping said volume limited wave whereby the amplitude of said shaped wave is dependent upon the frequency of said third wave, and means for rectifying said shapedwave to produce a signal the magnitude of which is also representative of the frequency of said third wave.

6. Thecombination of elements as in claim 1 in which said motor means comprises an armature, a first relay, a. second relay, a series field winding, a source of direct potential, means including the contacts of one of said`relays for connecting said series winding in one direction to said armature, and means including the contacts of said second relay for connecting said series winding in the opposite direction to said armature. A

7. Apparatus for accurately producing by the movement of a member at a sending station a desired predetermined movement of a member at a receiving station, comprising motor means for driving said member at the receiving station, circuit means for producing a signal controlled by, and corresponding to the position of. said sending station member, a. second circuit means for producing a signal controlled by, and corresponding to the position of said receiving station member, and means simultaneously differentially responsive to the magnitude of said two signals for actuating said motor means, each of said circuit means comprising means for deriving a voltage wave of fixed frequency, means for deriving a periodically varying voltage wave the frequency of variation of which is dependent at each instant upon the position of the one of said members controlling that circuitmeans, means for producing a wave the frequency of which is equal to the difference between said two frequencies, and means responsive to said last-mentioned wave for determining the magnitude of the signal produced in ,that circuit and controlling'said differentially re- Y sponsi've means.

' DOREN MITCHELL. 

